This invention relates to the automatic reading of utility and industrial meters such as gas, water and electric meters.
Many systems have been devised for automatically reading utility meters including the storing of input data obtained from the meters, and the readout of such data in response to interrogation from a remote data collecting station through telephone lines. Such a system is disclosed in U.S. Pat. No. 3,376,389 to Fair, owned by the assignee of the present application. Other prior U.S. patents more or less related to the subject matter of the present invention in regard to general objectives include U.S. Pat. Nos. 3,553,376, 3,588,357, 3,390,234, 3,747,068, 3,786,423, 3,800,091, 3,820,073, 3,842,206 and 3,868,640.
Prior automatic utility meter reading systems of the aforementioned type have not been generally adopted because of economic factors. Such factors include the cost of the system itself, the required modification of existing utility meters, the generation of signal carriers and dependence on telephone company equipment. It is therefore an immportant object of the present invention to provide an automatic meter reading unit of relatively low cost, having a complete receive/transmit capability to avoid dependence on equipment of the telephone utility and requiring relatively minor modification of the meters to be read.
In its most general application, the automatic reading unit of the present invention is operative to monitor a sequence of events represented by switch closures. Digital inputs are received in a digital circuit assembly in which counter logic stores data bits corresponding to said switch closures as well as an identification code bit and a power data bit representing the state of the power source through which the unit is energized. Operating power for the unit is obtained independently of the signal transmission lines to which it is connected. An analog polling signal when detected across the signal transmission lines, is demodulated into a digital poll code for interrogation purposes by initiating a transmit cycle during which the stored bits in the counter logic are serially readout and transformed by digital synthesizers into a step simulated sinusoidal waveform. This simulated waveform is converted into an analog data signal fed through the signal transmission lines to a data collecting station.
The automatic meter reading unit of the present invention is associated with a system wherein a plurality of utility meters at each meter reading station are modified by the mounting of magnetic elements on the dials of the meter for causing switch closures or reed switches during each revolution of each unit dial. The switch closures are sensed by electronic decade counters that are stepped to maintain or store digital input data corresponding to the meter readings represented by the switch closures. The automatic meter reading unit is powered by the usually available AC power source with a battery backup to maintain the counts and remote unit operation during a power outage. Information on the state of the power source is represented by a data bit in the transmitted code signal containing the data bits representing the meter reading inputs to the unit. Interrogation of the meter reading unit is accomplished by dispatch of coded polling signals to the meter reading unit from a central data collection station located, for example, at a utility company. Each meter reading station may be automatically dialed and upon sensing of the coded polling signal, the automatic meter reading unit responds by transmitting the aforementioned input data bits as well as the power bit and an identification code bit. A high impedance device such as an opto-isolator is bridged across the telephone lines at the meter reading station, to isolate the unit from the telephone line during its interrogation receive mode. In response to receipt of the proper poll code, the lines are seized at the meter reading station by the connection of a load thereacross through a reed relay circuit. The unit is then placed in its transmit mode with the bits of information stored in the digital counter logic serially readout and frequency shift modulated. The readout of the meter reading unit is synthesized into a step simulated sinusoidal waveform and converted into an analog signal conforming to requirements of the telephone communication system in regard to harmonic content and signal strength of the transmitted signal. Further, by producing a zero output at the beginning of each transmit cycle for a period of short duration data may be transmitted without generation of any signal carrier. The digital logic components associated with the automatic meter reading unit are integrated into a single large scale integrated circuit chip. This digital circuit assembly includes parity checking components for detecting poll code transmission signal error, which would result in an automatic reset. Various options are available to functionally enlarge the system with which the automatic reading unit is associated by relatively simple connection of additional components thereto including facilities to monitor time-of-day usage of the various utilities being automatically read, means for monitoring the meter reading inputs during spaced intervals of time for demand reading purposes and means for providing a remote control function at the meter reading station in association with the interrogation of the automatic meter reading unit. The foregoing options are significant in that they provide for low cost load management.
These together with other objects and advantages which will become subsequently apparent reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.